Up to now, ejectors have been known as a depressurizing device applied to a vapor compression refrigeration cycle device. The ejector of this type has a nozzle portion that depressurizes refrigerant, draws a gas-phase refrigerant which has flowed out of an evaporator due to a suction action of an ejection refrigerant ejected from the nozzle portion, mixes the ejection refrigerant with the suction refrigerant in a pressure increase part (diffuser portion), thereby being capable of increasing the pressure.
Accordingly, in a refrigeration cycle device (hereinafter, referred to as an ejector refrigeration cycle) including an ejector as a depressurizing device, power consumption of a compressor can be decreased using refrigerant pressure action in the pressure increase part of an ejector, and a coefficient of performance (COP) of a cycle can be further improved to a greater extent than a general refrigeration cycle device including an expansion valve or the like as a depressurizing device.
Further, Patent Document 1 discloses an ejector having the nozzle portion which depressurizes the refrigerant in two stages as the ejector applied to the ejector refrigeration cycle. In more detail, in the ejector of Patent Document 1, the refrigerant of a high pressure liquid-phase state is depressurized into a gas-liquid two-phase state in a first nozzle, and the refrigerant that has been the gas-liquid two-phase state flows into a second nozzle.
With the above configuration, in the ejector of Patent Document 1, boiling of the refrigerant in the second nozzle is promoted to improve a nozzle efficiency as the overall nozzle portion, and the COP is to be further improved as the overall ejector refrigeration cycle.
In the general ejector, a diffuser portion (pressure increase part) is coaxially arranged on an extension in an axial direction of the nozzle portion. In addition, Patent Document 2 discloses that a spread angle of the diffuser portion thus arranged is relatively reduced to enable an improvement in the ejector efficiency.
The nozzle efficiency means energy conversion efficiency when a pressure energy of the refrigerant is converted into a kinetic energy in the nozzle portion. The ejector efficiency means energy conversion efficiency as the overall ejector.
However, in the ejector of Patent Document 1, for example, a heat load of the ejector refrigeration cycle becomes low, and a pressure difference (a difference between a high pressure and a low pressure) between the pressure of a high-pressure side refrigerant and the pressure of a low-pressure side refrigerant in the cycle is reduced. As a result, the difference between the high pressure and the low pressure is depressurized by the first nozzle, and most of the refrigerant may not be depressurized in the second nozzle.
In this case, the nozzle efficiency by causing the gas-liquid two phase refrigerant to flow in the second nozzle is not improved. As a result, the refrigerant may not be sufficiently pressurized by the diffuser portion.
On the contrary, with the application of the diffuser portion having the relatively small spread angle disclosed in Patent Document 2 to the ejector of Patent Document 1 to improve the ejector efficiency, a method of pressurizing the refrigerant sufficiently in the diffuser portion even in the low load of the ejector refrigeration cycle is conceivable.
However, when the diffuser portion is applied, the length in the axial direction of the nozzle portion in the entire ejector increases, and thereby causes the possibility that a volume of the ejector may unnecessarily increase during a general load of the ejector refrigeration cycle.